Preparation of PVA/PEI/MWCNTs-COOH conductive hydrogels for strain sensors using a synergistic post-processing technique

Addressing the critical challenge of balancing mechanical robustness and electrical conductivity in hydrogels for wearable sensors, this study proposes a synergistic processing strategy that integrates freeze-thaw cycling, thermal annealing, and the Hofmeister effect-induced salting. A ternary composite hydrogel was prepared with polyvinyl alcohol (PVA) as the matrix, polyethyleneimine (PEI) to enhance crosslinking and biocompatibility, and carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) to improve conductivity. The optimized freeze-thawing-annealing (100 °C, 20 min) and salting-out (1.5 M NaCl) process resulted in a densely cross-linked network featuring significantly enhanced crystallinity and a homogeneous, pore-free microstructure. This hierarchical structure confers upon the hydrogel outstanding mechanical properties: tensile strength of 4.15 MPa, toughness of 17.73 MJ/m 3 , elastic modulus of 2.84 MPa, and a high fatigue threshold of 117.4 J/m 2 . Simultaneously, the electrical conductivity of the hydrogel reached 0.449 S/m. The hydrogel demonstrated excellent strain/pressure sensing capabilities, featuring tunable gauge factors (GF = 0.87–2.12 within the 0-100% strain range) and pressure sensitivity (0.145 kPa -1 below 2 kPa). The practical applicability of the hydrogel was verified by reliably monitoring various human motions in real-time. This research offers a scalable and effective material design strategy for next-generation flexible electronics.